Reinsurance - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) reinsurer	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Ceded Credit Risk [Line Items]
Premium ceded reduction amount	$ 7,100,000	$ 1,100,000	$ 15,700,000
Amount due from reinsurers total	$ 288,600,000
Number of major reinsurers | reinsurer	0
Allowance for reinsurance receivables	$ 0	0
Loss on uncollectible accounts in the period	0	0	0
Assumed premiums earned	37,805,000	22,691,000	$ 12,987,000
Cash receipt for reinsurance commutations	5,446,000	$ 9,249,000
Amount of reinsurance recoverables collateralized by letters of credit	48,500,000
Novation Agreement
Ceded Credit Risk [Line Items]
Assumed premiums earned	11,800,000
Minimum
Ceded Credit Risk [Line Items]
Major reinsurer threshold	26,000,000
Specialty P&C
Ceded Credit Risk [Line Items]
Cash receipt for reinsurance commutations	6,800,000
Amount of reinsurance recoverables collateralized by letters of credit	$ 7,100,000